Fluid coke agglomeration, calcination and desulfurization



I. SMITH ET AL FLUID COKE AGGLOME July 15, 1958 RATION, CALCINATION AND DESULFURIZATION Filed Sept. 9, 1954 m E Qz GE wzoN 23 m3 mo 46 wENEESwME wzoN wzcZm wzr25238 Qz 3:25 20 S ow 9 m E m2 9 NW $60 mmzmnm x3? 19:. 05 a \m Brook l. Smith By Fred w. Bones KGW Attorney United lFlLlUliD Ctl lifll AGGLQMERATION, CALCINATION AND DESULFUREZATION Application September 9, 1954, Serial No. 455,039

8 (Llairns. Cl. 202-412.)

This invention relates to improvements in agglomerating, calcining and desulfurizing coke particles from a fluid coking process. More particularly it relates to a process wherein these purposes are achieved by subjecting the fluid coke particles and a binder material to a tumbling motion on a rotary supporting surface in a plurality of successive sections of increasing temperature.

There has recently been developed an improved process known as the fiuid coking process for the production of coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions. basically of a reaction vessel or coker and a heater or burner vessel. in a typical operation the heavy oil to be processed is injected into the reaction vessel containing a dense, turbulent, fluidized bed of hot inert solid particles, preferably coke particles. Uniform temperature exists in the coking bed. Staged reactors can be employed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the slipper to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the heater or burner vessel which preferably is a separate vessel. A stream of coke is transferred from the reactor to the burner vessel employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Sufficient coke or carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature sufficient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke, based on the feed, or an equivalent amount of an extraneous fuel such as natural gas or fuel oil is burned for this purpose. If coke is burned it may amount to approximately 15% to 30% of the coke made in the process. The unburned portion of the gross coke production represents the net coke formed in the process and is withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and vacuum crude bottoms, pitch, asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically such feeds can have an initial boiling point of about 700 F. or higher, an A. P. l. gravity of about to 20, and a Conradson carbon residue content of about to 40 Wt. percent. (As to Conradson carbon residue see ASTM Test B48042.)

it is preferred to operate with solids having a particle size ranging between 40 and 1000 microns in diameter The fluid coking unit consists atent 'ice 2 With a preferred average particle size range between 150 and 400 microns. Preferably not more than 5% has a particle size below about microns, since small particles tend to agglomerate or are swept out of the system with the gases.

The method of fluid solids circulation described above is Well known in the prior art. Solids handling technique is described broadly in Packie Patent 2,589,124, issued March 11, 1952.

Fluid coking has its greatest utility in upgrading the quality of low grade petroleum vacuum residua and pitches from highly asphaltic and sour crudes. Such re sidua frequently contain high concentrations of sulfur, i. e., 3 wt. percent or more and the coke product produced from. these high sulfur feeds is also high in sulfur content. In general the sulfur content of the coke product from the fluid coking process is about 2 times the sulfur content of the residuum feed from which it is produced. The sulfur content of coke from sour residua can range from 5% to 8% sulfur or more. The high sulfur content of the coke product poses a major problem in its efiicient utilization. For most non-fuel or premium fuel uses a low sulfur content coke, below about 3 wt. percent sulfur is required. For example, low sulfur content coke is desired for the manufacturs of phosphorous, for the production of calcium carbide, for lime burning in the manufacture of soda ash or other alkalis, for various metallurgical application, and for the production of electrode carbon for various electrochemical applications such as the manufacture of aluminum and the like.

Another problem in the marketing of the fluid coke product is that the particle diameter is predominantly, i. e., about 60-90 wt. percent, in the range of 150 to 850 microns diameter. The production of substantially larger particles is inconsistent with satisfactory operation of the fluid bed. On the other hand industrial requirements for coke necessitate particles having a diameter of about at least A; inch to 1 inch.

This will permit subsequent grinding to give the desired particle size range which includes coarse as well as fine particles. For certain uses, as in the preparation of carbon electrodes for aluminum purification, the coke in addition to having an increased particle size must also be calcined and desulfurized. It is preferred that the fluid coke used for this purpose be calcined to a satisfactorily low volatile content of less than 0.5% and a real density of at least 1.85 g./ml. It is also preferred that the coke be desulfurized to a sulfur content of 3% or less, for eX- ample, 2%.

This invention provides an improved method for improving the beforementioned characteristics; of the fluid coke. The method comprises subjecting a charge of an agglutinating carbonaceous substance and uncalcined fluid coke to a tumbling motion on a rotary supporting surface, e. g., in a rotary kiln, utilizing a plurality of successive sections of increasing temperatures. The details of these sections and their temperatures are elaborated upon below. The mixture is thus heated on its downward path through the kiln to successively higher temperatures. Agglomeration or pelletization, calcination and desulfurization are thereby obtained.

The agglutinating carbonaceous substances, which are liquid at the temperature of the agglomerization zone, that can be utilized include suitable hydrocarbon binders, such as crude petroleum, petroleum residues, aromatic tars, e. g., vacuum reduced thermal tars, heavy ends of coal tar, such as coal tar pitches having a minimum softening point of about C., and heavy ends from the coking operation, i. e., 1050 F.-|- material. These substances are utilized in an amount of about 5 to 40 weight based on the coke charge and preferably 10 asaaeas to 30 weight The fluid coke can be used in the usual particle size range although it may be preferable to grind a portion of it to provide 20% to 50% of the coke aggregate as less than 75 micron material.

The rotary kiln which operates at a peripheral speed of 100 to 500 ft./min. is divided according to the temperatures utilized into three functional sections: (1) an agglomerating section, (2) a baking section, and (3) a calcining desulfurizing section.

The agglomerating section into which the coke and binding substance are charged is the coolest section and is maintained at a temperature of 250 to 1000 F, preferably 300 to 750 P. On its way through this section, where it is retained for 5 to 60 minutes, preferably to 30 minutes, the coke is uniformly impregnated with the binder so as to become agglutinated. As a result of the rotary motion of the kiln, the coke agglomerates to form spheroidal or ball-shaped coke pellets varying in size from about A to about 2 in diameter.

The agglomerated coke particles pass on their downward path through the rotary kiln into the next baking section wherein the prevailing temperature is in the range of about 1000 to 1800 F. and the contact time is in the range of to 60 minutes. The binder is further coked and most volatiles removed. This prepares a firm carbon bond cementing together the agglomerated coke particles and thereby imparting high mechanical strength. Otherwise plastic flow and sticking would be encountered.

The baked agglomerates are then passed finally into a calcining and desulfurizing section wherein a temperature range of about 1700 to 2700 F., preferably 2100 to 2600 F. is encountered. The residence time in the calcining section is in the range of about 10 minutes to 4 hours, preferably 15 minutes to 120 minutes. The calcining increases the density of the coke, lowers the volatile content and electrical resistivity and decreases the sulfur content to less than 3 weight percent.

The indicated temperatures in the different sections are obtained by controlled combustion at the hot end or calcining section of the kiln of a carbonaceous substance. The combustible material can be a portion of the coke but more preferably it is an extraneous fuel such as fuel oil or natural gas or high temperature flue gas supplied from an auxiliary burner. The combustion is supported through the presence of an oxygen-containing gas such as air. The highest temperature is thus maintained in the calcining section and the lower temperatures in the preceding sections supplied by the hot combustion gases.

This invention will be better understood by reference to an example and flow diagram shown in the drawing.

In the drawing the numeral 1 diagrammatically represents a rotary kiln containing an agglomerating section 10, a baking section 20, and a calcining and desulfurizing section 30. 100 parts by weight of fluid coke of 40 to 1000 microns diameter, containing 80% of material with diameters in the range of 150 to 850 microns, and con taining 7 wt. percent sulfur, is charged into the agglomerating section 10 through line 2. parts by weight of a vacuum reduced thermal tar from the cracking of a catalytic clarified oil is introduced into the same section through line 3. This section is maintained at an average temperature of 750 F. and the coke is retained here for about 15 minutes. Here the coke and tar are rolled into balls or spheroidal coke agglomerates by the tumbling motion on the rotary supporting surface and the partial carbonization of the agglutinating substance that takes place at the specified temperature.

The coke agglomerates on the downward path pass into the baking section 20 which is at a temperature of about 1700 F. at the exit or lower end of the section. The coke agglomerates remain in the baking section for about minutes. Further carbonization of the binder and loss of plasticity takes place.

The baked agglomerates now pass on their downward 4 path into the calcining and desulfurizing section 30 which has a temperature gradient from the coolest to the hottest portion of 1800 to 2500 F. Natural gas together with air is introduced into the lower end of calcining section 30 through line 4. The natural gas is burned to carbon monoxide at the temperature in the calcining section.

The cool carbon monoxide flue gas withdrawn from the upper end of the rotary kiln can then be burned to predominantly carbon dioxide in an external heater which is employed to preheat the air and natural gas to about 1000 F. before being introduced at the lower end of the calcining section. This improves the heat economy of the process. The calcining is conducted for about minutes. This removes a substantial portion of the sulfur and also obtains the other advantages of calcining. The hot combustion gases of the burning operation heat the other two sections and provide the desired temperatures. The combustion gases in which carbon monoxide is present, together with the volatile material removed from the agglutinating substance pass out of the cool end of the kiln through line 5. The combustion gases also contain the sulfur removed as CS and 608 which are also removed at this point.

The treated and calcined product coke is removed from the hot end of the kiln through line a and can be cooled by direct water quench or other means known in the art. The product coke has a volatile content about 0.3%, a sulfur content of about 2.3 weight and a particle size predominantly in the range of A2" to 2".

The kiln can be readily constructed to accomplish the purpose disclosed. Thus, longitudinal fins are provided in the calcining section of the kiln to cause scattering of the coke particles, thereby bringing them into more intimate contact with the treating gas. Suitable circumferential rings or dams may be provided around the inside periphery of the kiln at appropriate points to provide the desired coke residence time for pelletizing, baking and calcining.

The conditions usually encountered in a fluid coker are also listed below so as to further illustrate how the coke was prepared.

Conditions in fluid coker reactor The advantages of this invention will be apparent to the skilled in the art. An integrated, efiicient process is provided for agglomerating, desulfurizing and calcining fluid coke.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. In a process for agglomerating, calcining and desulfurizing fluid coke containing a high percentage of sulfur by subjecting a charge of the fluid coke and an agglutinating carbonaceous substance to a tumbling motion on a rotary supporting surface the improvement which comprises providing a plurality of successive sections of increasing temperatures comprising in successive order an agglomerating section, a baking section and a calcining and desulfurizing section, the charge being introduced into the agglomerating section maintained at a temperature in the range of 250 to 1000 F. to eifect formation of spheroidal coke agglomerates and partial carbonization of the agglutinating substance, passing the coke agglomerates to the baking section wherein they are maintained at a temperature of 1000 to 1800 F. to completely carbonize and devolatilize the agglutinating substances and passing the baked agglomerates to the calcining section wherein they are maintained at a temperature in the range of 1800 to 2700 F. by the combustion of a carbonaceous fuel material with an oxygencontaining gas for a period of time in the range of minutes to 4 hours, the heat of the agglomerating and baking sections being supplied by the combustion gases evolved in the calcining section and withdrawing agglomerated and desulfurized coke product.

2. The process of claim 1, in which the time of treat ment in the agglomerating section is in the range of 10 to 30 minutes, in the baking section in the range of to 60 minutes, and in the calcining section in the range of 15 to 120 minutes.

3. The process of claim 2 including the additional step of withdrawing carbon monoxide containing flue gas from the agglomerating section and burning this carbon monoxide in an external heating zone with additional oxygen-containing gas so as to preheat the carbonaceous fuel material and oxygen-containing gas, the combustion of which supplies heat to the calcining section.

4. The process of claim 3 in which the carbonaceous fuel material is natural gas.

5. The process of claim 2 in which the fluid coke charge has a particle diameter predominantly in the range of 150 to 850 microns and the agglomerated coke product has a particle diameter of A3" to 2".

6. The process of claim 5 in which the amount of the agglutinating carbonaceous substance utilized is in the range of 5 to weight percent based on the fluid coke.

7. The process of claim 5 in which the agglutinating substance is a vacuum reduced thermal tar.

8. The process of claim 5 in which the agglutinating substance is a coal tar pitch having a minimum softening point of about C.

References Cited in the file of this patent UNITED STATES PATENTS 1,732,219 Bjerregaard Oct. 22, 1929 1,912,629 Fisher June 6, 1933 1,948,471 Loebell et al. Feb. 20, 1934 2,462,366 Davies et al. Feb. 22, 1949 2,511,709 Hemminger June 13, 1950 2,560,357 Martin et al. July 10, 1951 2,650,190 Steinschlaeger Aug. 25, 1953 2,664,389 Rex et al. Dec. 29, 1953 2,709,676 Krebs May 31, 1955 FOREIGN PATENTS 676,494 Great Britain Aug. 23, 1950 690,791 Great Britain Aug. 24, 1951 

1. IN A PROCESS FOR AGGLOMERATING, CALCINING AND DESULFURIZING FLUID COKE CONTAINING A HIGH PERCENTAGE OF SULFUR BY SUBJECTING A CHARGE OF THE FLUID COKE AND AN AGGLUTINATING CARBONACEOUS SUBSTANCE TO A TUMBLING MOTION ON A ROTARY SUPPORTING SURFACE THE IMPROVEMENT WHICH COMPRISES PROVIDING A PLURALITY OF SUCCESSIVE SECTIONS OF INCREASING TEMPERATURES COMPRISING IN SUCCESSIVE ORDER AN AGGLOMERATING SECTION, A BAKING SECTION AND A CALCINING AND DESULFURIZING SECTION, THE CHARGE BEING INTRODUCED INTO THE AGGLOMERATING SECTION MAINTAINED AT A TEMPERATURE IN THE RANGE OF 250* TO 1000*F. TO EFFECT FORMATION OF SPHEROIDAL COKE AGGLOMERATES AND PARTIAL CARBONIZATION OF THE AGGLUTINATING SUBSTANCE, PASSING THE COKE AGGLOMERATES TO THE BAKING SECTION WHEREIN THEY ARE MAINTAINED AT A TEMPERATURE OF 1000* TO 1800*F. TO COMPLETELY CARBONIZE AND DEVOLATILIZE THE AGGLUTINATING 